In order to achieve a high efficiency, a high turbine inlet temperature is used in standard gas turbines. As a result, there arise high NOx emission levels and higher life cycle costs. This can be mitigated with a sequential combustion cycle, wherein the compressor delivers nearly double the pressure ratio of a known one. The main flow passes the first combustion chamber (e.g. using a burner of the general type as disclosed in EP 1 257 809 or as in U.S. Pat. No. 4,932,861, also called EV combustor, where the EV stands for environmental), wherein a part of the fuel is combusted. After expanding at the high-pressure turbine stage, the remaining fuel is added and combusted (e.g. using a burner of the type as disclosed in U.S. Pat. Nos. 5,431,018 or 5,626,017 or in U.S. Patent Application Publication No. 2002/0187448, also called a SEV combustor, where the S stands for sequential). Both combustors contain premixing burners, as low NOx emissions involve high mixing quality of the fuel and the oxidizer.
SEV-burners can be designed for operation on natural gas and oil only. The subsequent mixing of the fuel and the oxidizer at the exit of the mixing zone can be just sufficient to allow low NOx emissions (mixing quality), to avoid thermo-acoustic pulsations and to avoid flashback (residence time).